Loudspeaker and Assembly of Loudspeakers

ABSTRACT

A loudspeaker comprising a magnet unit that generates a magnetic field and a membrane which is mounted in a frame and which is provided with an electrical conductor arranged in a pattern on the membrane, which membrane is positioned in the magnetic field in such a manner that a force is exerted when current is fed through the conductor pattern on the membrane, which force is capable of setting the membrane vibrating to produce sound, said loudspeaker being provided with a sound opening located between the vibrating region and the outer side of the loudspeaker, which sound opening connects to a sound horn having diverging walls, characterized in that substantially identical sound openings and sound horns connecting thereto extend on both sides of the membrane.

TECHNICAL FIELD

The invention relates to a loudspeaker comprising a magnet unit thatgenerates a magnetic field and a membrane which is mounted in a frameand which is provided with an electrical conductor arranged in a patternon the membrane, which membrane is positioned in the magnetic field insuch a manner that a force is exerted when current is fed through theconductor pattern on the membrane, which force is capable of setting themembrane vibrating to produce sound, said loudspeaker being providedwith a sound opening located between the vibrating region and the outerside of the loudspeaker, which sound opening connects to a sound hornhaving diverging walls.

Such a loudspeaker is disclosed in International patent applicationPCT/NL2004/00159 (not published).

PRIOR ART

The invention is in particular aimed at providing an improvedloudspeaker for applications in which a directed, narrow, elongate soundrange is desired. Think in this connection of railway station platforms,for example, both in the open air and indoors, or underground, such asin underground stations. The sound horns of the loudspeakers may bedirected in the longitudinal direction of the platform in order todirect the sound as much as possible at the location where travellersare waiting.

Two major problems occur with these loudspeakers. In general, a soundhorn only suppresses sound in lateral direction to a limited degree. Asa result, sound will nevertheless permeate in lateral direction, andthus into the environment, on open-air platforms. In particular in anurban environment this causes nuisance for the people living in theneighbourhood. In addition, it leads to unnecessary energy consumption,because the sound does not reach its intended destination, viz. thewaiting public. On indoor platforms or in underground stations, thesound that has permeated in lateral direction reflects from the walls,which leads to a great deal of reverberation, making it difficult tocatch what is being said. Furthermore, the aiming effect of the horns islimited to a restricted frequency range.

The invention is not limited to the above applications, however, and canbe used advantageously, for example, in any application in which thelistener is removed relatively far from the loudspeaker in comparisonwith nearby surfaces such as a wall, a ceiling or a floor, which canreflect sound, or in comparison with nearby areas where the presence ofsound is undesirable.

The object of the invention is to provide a loudspeaker of the kindreferred to in the introduction which, in particular in applicationswhich aim at realising an elongate or a very specific range, diminishesthe above-described effects in a simple and efficient manner and/orwhich exhibits better acoustic characteristics than the knownloudspeakers.

DESCRIPTION OF THE INVENTION

In a loudspeaker according to the invention, substantially identicalsound channels and sound horns connected to said channels extend oneither side of the membrane. Not only is sound emitted in two directionsin a very efficient manner in this way, but in addition sound thatpermeates to the sides dies out entirely or partially as a result of thefact that the permeating sound waves emanating from the two sound hornsare automatically in counter phase as a result of this construction. Inthis way a very well-directed and energy-efficient sound reproduction isachieved for a large frequency range. This may be advantageous for alarmloudspeakers as well, because such loudspeakers are frequently poweredby batteries or by an emergency power unit, and because of said energyefficiency such power sources can be designed to be as small and thus asinexpensive as possible.

US patent application US-A-2004/0,047,488 discloses a loudspeakercomprising identical sound channels that extend on either side of themembrane. The sound that is emitted at the rear side of the membrane iseventually aimed at the front side via reflection. Said loudspeaker isnot suitable for applications in which the goal is to achieve a highlycontrolled aiming effect, therefore, and consequently the loudspeakerdoes not have a sound horn.

Preferably, the loudspeaker is a magnetostatic ribbon loudspeaker whosemembrane is a flat membrane in which the conductor pattern isintegrated, with the sound openings being formed by sound channels. Theinvention can also be used with electrostatic loudspeakers, for example,and can be advantageous even with dome and cone loudspeakers.

Preferably, the sound horns have an elongate, e.g. rectangular or ovalcross-section, making it possible to direct the sound separately inhorizontal and in vertical direction. Preferably, the central axes ofthe sound horns, which are located between the upper wall and the lowerwall, extend at an acute angle with respect to the membrane. Forexample, the central axes extend downwards at an angle with respect tothe membrane, so that the sound is quite audible also directly below theloudspeaker and the sound need not be directed over the heads of thepublic.

Preferably, the central axes of the two sound channels of theloudspeaker, which are located between the outer wall and the inner wallof each channel, incline towards each other over a particular distancefrom the membrane. The term central axis of a sound channel isunderstood to mean the imaginary centre plane that lies preciselybetween the inner wall and the outer wall of the channel. In this waythe wavefronts of the two sound sources are gradually directed towardseach other and combined upon exiting the sound channels. The aforesaidlobing effect is thus largely prevented. Preferably, the outer walls ofthe two sound channels that are spaced furthest apart incline towardseach other over a particular distance from the membrane and, likewisepreferably, the inner walls of the two sound channels that lie closesttogether likewise incline towards each other over at least a particulardistance from the membrane. Even more preferably, the inner and outerwalls of each sound channel extend substantially parallel to each other.

The distance over which the walls incline towards each other ispreferably at least 0.5 times, preferably at least 1 time the width ofthe sound channels. Furthermore, the spacing between the inner walls ofthe sound channels on the outer side of the housing is preferably lessthan 0.5 times, preferably less than 0.2 times the spacing between theinner walls on the side of the membrane. In this way the two wavefrontsare combined in the most gradual way that is possible.

Preferably, the outer walls of the sound channels join the walls of asound horn comprising diverging walls near their ends, as a result ofwhich the combined way front initially widens in a controlled andmoreover directed manner.

The invention further relates to an assembly of loudspeakers, wherein anumber of loudspeakers are arranged in substantially alignedrelationship, wherein the sound horns of two adjacent loudspeakers aredirected substantially towards each other, and wherein the facingsurfaces of the membranes of two adjacent loudspeakers are in phase(with the two surfaces simultaneously moving towards the listener andaway from the listener, therefore). Preferably, the central axes of twosound ports that face towards each other are directed at a point locatedapproximately at ear level precisely between the two loudspeakers. Theaiming effect can be influenced by varying the position of the hornswith respect to each other, e.g. directly opposite each other orinclined further towards each other on one side, and also the shape ofthe horn.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail by means of adescription of embodiments that are shown in the Figures, in which:

FIG. 1 is a partial perspective view of a loudspeaker;

FIG. 2 is a cross-sectional view of the loudspeaker of FIG. 1;

FIG. 3 is a cross-sectional view of the loudspeaker of FIG. 1, on whicha sound horn is mounted;

FIG. 4 is a perspective view of a membrane unit; and

FIG. 5 is a cross-sectional view of a loudspeaker on which a sound hornis mounted on two sides.

EMBODIMENTS OF THE INVENTION

According to FIG. 1, a loudspeaker comprises a housing consisting of twosubstantially identical metal parts 1, 2, which are mounted together bymeans of screws 3. Each housing part 1, 2 has two elongate slot-shapedrecesses or sound channels 4, 5, which enable the sound that isgenerated in the loudspeaker to propagate towards the outside.Furthermore, a housing part 1 is provided with electrical terminals 6,7, to which the sound signal wires of an amplifier can be connected. Thehousing 1, 2 is provided with cooling fins 8 extending outwards and inthe longitudinal direction, which function to dissipate the heat that isgenerated in the loudspeaker.

The housing parts 1, 2 enclose a frame that is shown in FIG. 2, whichconsists of a first frame-shaped frame member 9 and two strip-shapedframe members 10, 11 (shown in FIG. 4). The frame members 9, 10, 11 arepreferably made of copper or anodised aluminium. The outer surface ofthe frame members 9, 10, 11 is in contact with the housing 1, 2 over theentire region thereof. A vibrating membrane 12 is affixed to the framemember 9 by means of a glue or by means of a thin, double-coatedadhesive tape. The glue or the tape is of a heat-conducting type. Anelectrical conductor pattern 13 is arranged on the membrane 12, whichconductor pattern is connected to the terminals 6, 7 and which causesthe-membrane to vibrate when the amplifier transmits an electric signalto the loudspeaker.

To that end the loudspeaker comprises magnets 13, as shown in FIG. 3,which generate a permanent magnetic field encompassing the conductorpattern 14 of the membrane 12. The conductor pattern 14 is formed by anelectrically conducting wire, which is arranged in an elongate,rectangular spiral on one side of the membrane 12. At the short sides ofthe rectangular pattern, the frame members 10, 11 are mounted directlyon the conductor pattern. Consequently, the glue or the tape by means ofwhich said members are affixed to the conductive wire must beelectrically insulating. On the other side of the membrane 12, saidshort sides of the pattern are likewise covered, in this case by theshort sides of the frame-shaped frame member 9. This arrangement enablesthe conductor pattern 14 to transfer heat to the frame members 9, 10, 11on both sides.

The two ends of the conducting wire are connected to power terminals 15,16 on the frame member 10, which are in turn electrically connected tothe terminals 6, 7. The power terminals 15, 16 are electricallyinsulated from the frame member 10. The lines of the conductor pattern14 that extend parallel to each other in the longitudinal directionbetween the frame members 10, 11 form two spaced-apart vibrating regions17, 18.

With reference now to FIG. 3, the sound channels 4, 5 extend from aposition located near the two spaced-apart vibrating regions 17, 18 onthe surface of the membrane 12 to the outer side of the housing parts 1,2, on one side the sound channels 4, 5 are closed by a closing plate 25,however, because the loudspeaker must emit the sound in only onedirection. The sound channels 4, 5 initially extend perpendicularly tothe membrane, seen from the membrane, viz. in the area between themagnets 13, and subsequently the sound channels 4, 5 incline towardseach other. Both the outer walls 19 and the inner walls 20 of each issound channels 4, 5 extend obliquely towards each other, with the innerwalls 19 and the outer wall 20 of a sound channel 4, 5 continuing toextend parallel to each other. On the outer side of the loudspeaker,only a very small spacing remains between the inner walls 19 of the twosound channels 4, 5, which spacing is at least several times smallerthan the spacing between the vibrating regions 17, 18. In this way thefronts of the sound waves that are generated by the two vibratingregions 17, 18 are directed towards each other and combined, thuspreventing disadvantageous interference between the two wavefronts.

FIG. 4 shows a sound horn 21, which is mounted in screw holes 24 of theloudspeaker by means of screws 23. The outer walls 19 of the soundchannels 4, 5 join the walls 22 of the sound horn 21. The sound horn 21effects a gradual widening of the sound front that emanates from thesound channels 4, 5 before it widens further into the environment. Thehorn, which is made of a metal, contributes to the heat dissipation ofthe loudspeaker.

According to FIG. 5, a loudspeaker comprises a loudspeaker 1, 2 as shownin the preceding Figures, in this case, however, a sound horn 21 ismounted to either side of the membrane. The closing plate 25 of FIGS. 3and 4 has been replaced by a second sound horn 21, therefore. Thefigures do not show that the sound horns 21 have a rectangularcross-section. As FIG. 5 shows, the central axes of the sound horns 21,which are located between the upper wall 22 a and the lower wall 22 b,extend downwards at an angle from the membrane 12.

1. A loudspeaker comprising a magnet unit (13) that generates a magneticfield and a membrane (12) which is mounted in a frame (9, 10, 11) andwhich is provided with an electrical conductor arranged in a pattern(14) on the membrane (12), which membrane is positioned in the magneticfield in such a manner that a force is exerted when current is fedthrough the conductor pattern (14) on the membrane (12), which force iscapable of setting the membrane (12) in motion so as to produce sound,said loudspeaker being provided with a sound opening (4, 5) locatedbetween the vibrating region (17, 18) and the outer side of theloudspeaker, which sound opening (4, 5) connects to a sound horn (21)having diverging walls, characterized in that substantially identicalsound openings (4, 5) and sound horns (21) connecting thereto extend onboth sides of the membrane.
 2. A loudspeaker according to claim 1,wherein the membrane (12) is a flat membrane in which the conductorpattern (14) is integrated, and wherein the sound openings are formed bysound channels (4, 5).
 3. A loudspeaker according to claim 1, whereinthe sound horns (21) have an elongate, e.g. rectangular or ovalcross-section.
 4. A loudspeaker according to claim 1, wherein thecentral axes of the sound horns (21), which are located between theupper wall (22 a) and the lower wall (22 b), extend at an acute anglewith respect to the membrane (12).
 5. A loudspeaker according to claim1, wherein the conductor pattern (14) is arranged on the membrane (12)in at least two spaced-apart vibrating regions (18, 18), wherein theloudspeaker is provided with at least two sound channels (4, 5), whichextend between the two vibrating regions (17, 18) and the outer side ofthe housing (1, 2).
 6. A loudspeaker according to claim 5, wherein thecentral axes of two sound channels (4, 5), which are located between theouter wall (19) and the inner wall (20) of each channel, incline towardseach other over a particular distance from the membrane (12).
 7. Aloudspeaker according to claim 5, wherein the outer walls (19) of thetwo sound channels (4, 5) that are spaced furthest apart incline towardseach other over at least a particular distance from the membrane (12).8. A loudspeaker according to claim 5, wherein the inner walls (20) ofthe two sound channels (4, 5) that lie closest together incline towardseach other over at least a particular distance from the membrane (12).9. A loudspeaker according to claim 5, wherein the inner and outer walls(19, 20) of each sound channel (4, 5) extend substantially parallel toeach other.
 10. A loudspeaker according claim 5, wherein the outer walls(19) of the sound channels (4, 5) join the walls (22) of the sound horns(21) near their ends.
 11. An assembly of loudspeakers, wherein a numberof loudspeakers according to claim 1 are arranged in substantiallyaligned relationship, wherein the sound horns (21) of two adjacentloudspeakers are directed substantially towards each other, and whereinthe facing surfaces of the membranes (12) of two adjacent loudspeakersare in phase.